Thermal change detector of the linear thermopile type

ABSTRACT

An improved thermal change detector of the linear thermopile type is disclosed. A transient temperature differential between adjacent thermopile junctions is obtained by shaping each link in the linear thermopile asymmetrically and joining them so that the thermal capacity of the &#39;&#39;&#39;&#39;hot&#39;&#39;&#39;&#39; junctions is smaller than that of the &#39;&#39;&#39;&#39;cool&#39;&#39;&#39;&#39; junctions. When a rapid rise occurs in the temperature of the environment, as for example when a fire breaks out, the &#39;&#39;&#39;&#39;hot&#39;&#39;&#39;&#39; junctions, having less thermal capacity, heat up more quickly than the &#39;&#39;&#39;&#39;cool&#39;&#39;&#39;&#39; junctions. This produces an electric potential across the thermopile which may be used to trigger alarm circuitry.

nited States Patent Matsui Feb. 22, 1972 [54] THERMAL CHANGE DETECTOR OF2,502,399 3/ 1950 Greetf ..136/2l1 X THE LINEAR THERMOPILE TYPE PrimaryExaminer-Donald J. Yusko [72] inventor. Masatoshi Matsui, Tokyo-to,Japan Assistant Examiner wimam wannisky [73] Assignee: Asano Bosai KogyoKabushikl Kalsha, Attorney-Davis, Hoxie, Faithfull & Hapgood Mitaka-shi,Tokyo-to, Japan 221 Filed: Dec. 16, 1969 [57] ABSTRACT An improvedthennal change detector of the linear thermopile [21] Appl' 885505 typeis disclosed. A transient temperature differential between adjacentthermopile junctions is obtained by shaping each link [52] U.S.Cl...340/228 R, 136/211, 136/223, in the linear thermgpile asymmetricallyand joining them so l36/224 that the thermal capacity of the hot"junctions is smaller than [51] Int. Cl ..G0lk 7/02, HOlv l/32 that ofthe p junctions w a rapid rise occurs i the [58] Field of Search..340/228, 227; 136/208, 211, temperature of the environment, as forexample when a fire 136/212 216 breaks out, the hot junctions, havingless thermal capacity, heat up more quickly than the cool junctions.This produces [56] References cued an electric potential across thethermopile which may be used UNITED STATES PATENTS to trigger alarmcircuitry.

2,956,267 10/ 1 960 Matthews ..340/228 X 10 Claims, 2 Drawing FiguresPatented Feb. 22, 1972 3,644,913

FIG. I.

FIG. 2.

BACKGROUND OF THE INVENTION There are presently several varieties ofcommercially available thermal change detecting systems. A first kind,known as the pneumatic type, comprises a relatively thin andinconspicuous copper pipe containing a metal diaphragm. The pipe is openon one side of the diaphragm to room pressure and on the other side,through a breather valve, to a relatively constant temperaturereservoir. Increased room air pressure resulting from a fire or othercause of thermal change causes bowing of the diaphragm, bowing which isaccentuated by the back pressure relief provided by the breather valve.Appropriate alarm circuitry is triggered by a predetermined amount ofdiaphragm movement.

This variety of thermal change detector, however, has several drawbacks.The metal diaphragm can become distorted with age, and the sensitivityof the device may be seriously affected by changes in the reservoirtemperature. Therefore, while the pneumatic type detector may berelatively inoffensive to the appearance of the protected room, it hassignificant functional deficiencies.

A second variety of thermal change detection system utilizes thermallygenerated electric voltages for its operation. These devices rely on thephysical phenomenon known as the Seebeck effect: that an electricpotential is developed between two junctions of many dissimilar metalsor metal alloys if the temperatures of those junctions are caused todiffer. The simplest arrangement of this type, where a strip of onemetal, commonly iron, is joined at each end to a strip of a secondmetal, commonly the alloy constantan, is called a thermocoupie. Thevoltages produced across such a thermocouple are on the order ofa fewmillivolts.

When a number of thermocouples are arranged in series with alternatinghot and cold junctions, the resulting array is called a thermopile. Thevoltage generated in a thermopile for a given temperature differentialwill be an appropriate multiple of the thermocouple voltage produced bythe same differential.

One form of thermopile-type thermal change detector in use comprises asuccession of interconnected wire pieces or links, alternately iron andconstantan, having every other junction covered with an insulatingmaterial such as vinyl chloride. If such a thermopile is mounted on aceiling, in case of fire or other cause of thermal change theuninsulated junctions will be heated to a temperature above that of theinsulated junctions, producing a voltage across the thermopile which canbe used to trigger appropriate alarm circuitry.

There are, however, at least two deficiencies in this form of detectionapparatus. First, in an age where interior design is consideredimportant, the appearance presented by this uneven contour mounted onthe ceiling is undesirable. Second, because of the uneven surface of thecomplete thermopile, some portions thereof may touch the ceiling whileother portions may not. This will cause the thermal capacities of thejunctions to be nonuniform and will thereby change the operatingcharacteristics of the device.

SUMMARY OF THE INVENTION The present invention concerns an improved formof thermopile-type thennal change detector which has a neat,inconspicuous appearance and provides accurate, reliable fire detection.The invention comprises a plurality of serially connected thermopiles,each constructed according to an improved, novel design. The hotjunctions in each of the thermopiles are composed of tubular sections ofthe two metals or metal alloys used, and the cool junctions are composedof solid sections of the same. The complete thermopiles are wrapped in aprotective, decorative coating and are connected in series with eachother and with suitable alarm circuitry.

DESCRIPTION OF THE FIGURES FIG. 1 is a sectional view of a thermopileconstructed according to the teachings of the present invention.

FIG. 2 is a diagram illustrating one possible ceiling arrangement ofthermopiles of the present invention.

DETAILED DESCRIPTION Referring now to those Figures, the linearthermopile shown in FIG. 1 is built around a number of iron links 1 andan equal number of constantan links 2 arranged in alternating sequence.Each of links 1 and 2 is cylindrical in shape, roughly 20 millimeters inlength and 1.6 millimeters in outer diameter. One-half of each link issolid, but the other half is tubular, with an axial cylindrical openingtherein roughly 1.2 millimeters in diameter and 10 millimeters deep. Thesolid ends of the iron and constantan links (6 and 5 respectively) arewelded together to form what will be the "cool" junctions 3 and thetubular ends (8 and 7 respectively) are likewise connected to form whatwill be the hot" junctions 4.

At each extremity of the linear thermopile thus formed, the open ends ofthe links are welded to electrical terminals such as copper connectors 9and 9'. These in turn are attached as shown in FIG. 2 to vinyl-coatedwire 12 which interconnects each thermopile with the remainder of thecircuit. The assembly is then, finally, covered with a vinyl coating 10forming a complete linear package 11 approximately 2 millimeters indiameter and, if l0 links each of iron and constantan are used, one-halfmeter in length.

One possible ceiling arrangement of 13 such thermopiles 11 is shown inFIG. 2, for even coverage ofa room approximately 10 by 15 meters. Thelinear thermopiles 11 are spaced about 5 meters apart in the roomceiling and are connected in series with each other and with a relay 13by wire 12. While the pattern shown provides substantially even coverageof the whole room, it is not the only possible arrangement; theinvention may be practiced in any desired pattern using any desirednumber of linear thermopiles 11.

In operation as a fire detector, a fire causes the temperature of theenvironment surrounding each thermopile 11 to rise quickly. Becausethose portions of the iron and constantan links adjacent to the hotjunction 4 are hollow, that junction will have a smaller thermalcapacity than cool junction 3. Therefore, while in the steady state bothjunctions will rise to the same temperature, the hot" junction 4 willexperience a transient temperature differential over the cool junction 3in the early moments of a fire, producing a voltage proportional to therate of rise of the room temperature.

Stated differently, although the two junctions have the same surfacearea, there is more mass present at junction 3 than at junction 4.Therefore, junction 3 will experience a lower rate of temperature risethan junction 4 for the same rate of heat transfer from the environment.This produces an output voltage which is used to trigger alarmcircuitry.

The thermopiles 1 1 must be connected, as shown in FIG. 2, with alltheir polarities oriented similarly. Relay I3 is adjusted to react whena certain total voltage appears.

Each thermopile built as described has the shape of a cylinder only avery few millimeters in diameter including a cover which can be chosenat least in part for appearance. It will not, therefore, be a visualintrusion on the decor of the room being protected. Because both sets ofjunctions are wrapped with the same amount of protective material, thelinear thermopile 11 does not have an uneven outer surface, and thisalso improves its appearance.

It should be added that the number, size, shape and composition of thethermopile links may be varied widely. As was suggested above, iron andconstantan are commonly used materials, but many combinations of metalsand metal alloys may be used. The only requirement is that thecharacteristics of the metals be such that when the detector issubjected to a thermal change, a nonzero net voltage appears across thethermopile. Furthermore, the sizes given are illustrative only, and itis clear that the links need not be cylindrical. Other modificationswill likewise be apparent to those skilled in the art which do notdepart from the spirit and scope of the present invention.

What is claimed is:

l. A thermal change detector comprising a plurality of first links of amaterial chosen from the group consisting of metals and metal alloys,

an equal number of second links of a different material chosen from saidgroup,

the first and second links being of equal dimensions and having equalportions of material removed from one end thereof to provide the one endwith a smaller thermal capacity than the other end,

the first and second links being arranged in alternate sequence with thesmaller thermal capacity ends joined together, means for completing anelectrical circuit connecting the first and last link in the sequence,

the materials of the first and second links being chosen so that whenthe detector is subjected to a thermal change a net voltage other thanzero appears across the links.

2. A thermal change detector as described in claim 1 wherein the lineararrangement of the links is covered by a protective coating.

3. A thermal change detector as claimed in claim 1 wherein the links arelinearly arranged in alternating sequence.

4. A thermal change detector as claimed in claim 1 wherein the links areshaped to have one solid end and one tubular end.

5. A thermal change detector as claimed in claim 1 wherein the firstlinks are made of iron and the second links of constantan.

6. A thermal change detection system comprising a plurality of spacedthermopiles wherein each of the thermopiles comprises a number of firstlinks of a material chosen from the group consisting of metals and metalalloys,

the same number of second links of a different material chosen from thesame group,

the first and second links being of equal dimensions and having equalportions of material removed from one end thereof to provide the one endwith a smaller thermal capacity than the other end,

the first and second links being linearly arranged in alternatingsequence with the smaller thermal capacity ends joined, the materials ofthe first and second links being chosen so that when the thermopile issubjected to a thermal change a net nonzero voltage appears across thethermopile,

the spaced thermopiles being interconnected in series bycircuit-completing means.

7. A thermal change detection system as described in claim 6 wherein thecircuit-completing means includes alarm means.

8. A thermal change detection system as described in claim 6 whereineach thermopile is covered by a protective coating.

9. A thermal change detection system as described in claim 6 wherein theone end of each link having a smaller thermal capacity is tubular andthe other end of each link having a larger thermal capacity is solid.

10. A thermal change detection system as described in claim 9 whereinthe circuit-completing means includes alarm means.

1. A thermal change detector comprising a plurality of first links of amaterial chosen from the group consisting of metals and metal alloys, anequal number of second links of a different material chosen from saidgroup, the first and second links being of equal dimensions and havingequal portions of material removed from one end thereof to provide theone end with a smaller thermal capacity than the other end, the firstand second links being arranged in alternate sequence with the smallerthermal capacity ends joined together, means for completing anelectrical circuit connecting the first and last link in the sequence,the materials of the first and second links being chosen so that whenthe detector is subjected to a thermal change a net voltage other thanzero appears across the links.
 2. A thermal change detector as describedin claim 1 wherein the linear arrangement of the links is covered by aprotective coating.
 3. A thermal change detector as claimed in claim 1wherein the links are linearly arranged in alternating sequence.
 4. Athermal change detector as claimed in claim 1 wherein the links areshaped to have one solid end and one tubular end.
 5. A thermal changedetector as claimed in claim 1 wherein the first links are made of ironand the second links of constantan.
 6. A thermal change detection systemcomprising a plurality of spaced thermopiles wherein each of thethermopiles comprises a number of first links of a material chosen fromthe group consisting of metals and metal alloys, the same number ofsecond links of a different material chosen from the same group, thefirst and second links being of equal dimensions and having equalportions of material removed from one end thereof to provide the one endwith a smaller thermal capacity than the other end, the first and secondlinks being linearly arranged in alternating sequence with the smallerthermal capacity ends joined, the materials of the first and secondlinks being chosen so that when the thermopile is subjected to a thermalchange a net nonzero voltage appears across the thermopile, the spacedthermopiles being interconnected in series By circuit-completing means.7. A thermal change detection system as described in claim 6 wherein thecircuit-completing means includes alarm means.
 8. A thermal changedetection system as described in claim 6 wherein each thermopile iscovered by a protective coating.
 9. A thermal change detection system asdescribed in claim 6 wherein the one end of each link having a smallerthermal capacity is tubular and the other end of each link having alarger thermal capacity is solid.
 10. A thermal change detection systemas described in claim 9 wherein the circuit-completing means includesalarm means.